Air trapping on computed tomography: regional versus diffuse.

Chronic obstructive pulmonary disease (COPD) is diagnosed and classified by spirometry, assessing the presence of airflow obstruction and extent of forced expiratory flow deterioration. Spirometry, however, is unsuitable for characterising and quantifying the underlying pulmonary pathology of COPD, including alveolar destruction (emphysema) and airway remodelling (largeand small-airway disease). Accurate diagnosis of the pulmonary pathologies underlying COPD is seen as an important step towards better understanding its biology and “personalised” treatment. Computed tomography (CT) of the lungs provides an excellent opportunity to assess COPD in vivo and quantify its macroscopic pathology [1–3]. Emphysema and airway remodelling can be visually assessed and automatically quantified, and several studies have shown associations with morbidity and mortality [4–7]. In addition, CT can provide information on the spatial distribution of disease.